Increasing Neutron Fluence Research Articles

Radiobiological evidence suggesting heterogeneous microdistribution of boron compounds in tumors: Its relation to quiescent cell population and tumor cure in neutron capture therapy

The heterogeneous microdistribution of boron compounds in tumors and its significance on tumor cure were examined by a radiobiological procedure. The role of quiescent (Q) cells in tumor was especially investigated. 10B-enriched paraboronophenylalanine (BPA) and mercaptoundecahydrododecaborate (BSH) were administered to SCCVII tumor bearing C3H/He mice by intragastric and i.v. injections, respectively. The continued effects of these boron compounds with thermal irradiations were studied by using colony formation and tumor control assays. Their effects on Q cells were also analyzed by the combined method of micronucleus frequency assay and an identification of proliferating (P) cells by BUdR and anti-BUdR monoclonal antibody. 10B-concentration after BPA (1,500 mg/kg) and BSH (75 mg/kg) administration were 11 ppm at 3 h and 10.5 ppm at 30 min, respectively. Cell survival decreased exponentially with an increment of neutron fluence (phi). The exponential parts of the curves were: -InSF = -0.052+ 13.0x10(13)phi, -InSF = -0.032+7.68X10(-13)phi, and -InSF = -0.0005+2.68x10(-13)phi for BPA-BNCT, BSH-BNCT, and NCT alone, respectively. Fifty percent tumor control was obtained at the influence of 10.2 x 10(12) n/cm2 in BPA-BNCT. On the other hand, 11.4 x 10(12) n/cm2 of neutrons had to be delivered in BSH-BNCT. The normal nuclear division fraction defined as the cell fraction that did not express micronuclei at first mitosis after treatment was investigated. The surviving cell fraction and the normal nuclear division fraction were regarded as equal in NCT alone. However, the normal nuclear division factor following BPA-BNCT was greater than the surviving cell fraction, and the difference increased with an increase in neutron fluence. In Q cells, BSH-BNCT yielded higher micronucleus frequency than BPA-BNCT and NCT alone. The frequencies in Q cells following BPA-BNCT and NCT alone were almost same as that in total cell population after NCT alone. Our data suggested that BPA distributed in tumors hetergeneously. Q cells especially might not accumulate BPA. To decrease the possible disadvantage of BPA-BNCT, the combination of BPA and BSH or other neutron capture element that emit particles with longer ranges, for example, gadolinium, would have to be investigated.

Enhanced flux pinning in HgBa2CuO4+x by neutron irradiation and its relationship to magnetic anisotropy

Our previous results indicate that neutron irradiation is an effective method for improving the pinning strength and critical current density of HgBa2CuO4+x, demonstrating that the mercury-based materials are not intrinsically limited to low current density. Here we expand our investigations of random HgBa2CuO4+x powders with a study of the effects of further neutron irradiation and annealing on the magnetization hysteresis and flux creep of powder samples. We also report the effects of irradiation on aligned powder samples and thus understand the relationship between flux pinning and magnetic anisotropy. We find that the critical current density continues to increase with increasing neutron fluence but at a decreasing rate. The irradiation enhancements in ground-then-aligned powders are not as large as in the as-sintered material, which we attribute to small defects introduced during the grinding process that inhibit the formation of defect clusters during irradiation. Lastly, we find that the neutron irradiation decreases and inverts the anisotropy as measured by magnetization hysteresis.

Change in physical properties of high density isotropic graphites irradiated in the “JOYO” fast reactor

Thirteen kinds of isotropic graphites with different density and maximum grain size were irradiated in the experimental fast reactor “JOYO” to fluences from 2.11 to 2.86 × 10 26 n/m 2 ( E > 0.1 MeV) at temperatures from 549 to 597°C. Postirradiation examination was carried out on the dimensional changes, elastic modulus, and thermal conductivity of these materials. Dimensional change results indicate that the graphites irradiated at lower fluences showed shrinkage upon neutron irradiation followed by increase with increasing neutron fluences, irrespective of differences in material parameters. The Young's modulus and Poisson's ratio increased by two to three times the unirradiated values. The large scatter found in Poisson's ratio of unirradiated materials became very small and a linear dependence on density was obtained after irradiation. The thermal conductivity decreased to one-fifth to one-tenth of unirradiated values, with a negligible change in specific heat. The results of postirradiation examination indicated that the changes in physical properties of high density, isotropic graphites were mainly dominated by the irradiation condition rather than their material parameters. Namely, the effects of irradiation induced defects on physical properties of heavily neutron-irradiated graphites are much larger than that of defects associated with as-fabricated specimens.

Void Formation in Magnesium Aluminate Spinel Heavily Irradiated with Fast Neutrons

Single crystals of magnesium aluminate spinel (MgAl2O4) were heavily irradiated to fission neutron fluences from −1 × 1026 to −2×1027 n/m2 (E>0.1 MeV) at 658 and 1,023 K in FFTF (Fast Flux Test Facility) to investigate their microstructural evolution under heavy neutron irradiation and to confirm their previously observed resistance to void swelling. At 658 K no voids were observed up to 2.29 × 1027 n/m2, but 1/4[110] interstitial loops were formed. These loops changed their habit planes from (111) to (110) with increasing neutron fluence. At 1,023 K the 1/4[110] type of interstitial loops grew to form stacking fault netuorks composed of stacking faults on each of the six equivalent (110) planes. Tiny voids were also observed to form preferentially on or near stacking faults after 1.37×1027 n/m2. A limited number of very small cavities, contributing to a volumetric swelling of only 0.07%, were also observed in the crystal matrix after 2.17×1027 n/m2. The possible mechanisms of suppression of void formatio...

Void Formation in Magnesium Aluminate Spinel Heavily Irradiated with Fast Neutrons.

Single crystals of magnesium aluminate spinel (MgAl2O4) were heavily irradiated to fission neutron fluences from −1 × 1026 to −2×1027 n/m2 (E>0.1 MeV) at 658 and 1,023 K in FFTF (Fast Flux Test Facility) to investigate their microstructural evolution under heavy neutron irradiation and to confirm their previously observed resistance to void swelling. At 658 K no voids were observed up to 2.29 × 1027 n/m2, but 1/4[110] interstitial loops were formed. These loops changed their habit planes from (111) to (110) with increasing neutron fluence. At 1,023 K the 1/4[110] type of interstitial loops grew to form stacking fault netuorks composed of stacking faults on each of the six equivalent (110) planes. Tiny voids were also observed to form preferentially on or near stacking faults after 1.37×1027 n/m2. A limited number of very small cavities, contributing to a volumetric swelling of only 0.07%, were also observed in the crystal matrix after 2.17×1027 n/m2. The possible mechanisms of suppression of void formation in MgAl2O4 are discussed.

Effects of neutron irradiation on microstructure and mechanical properties of carbon/carbon composites

As an important part of the national R&D program to high performance and low cost C C composite materials, a new manufacturing method of C C composite with densified matrix without conventional densification process has been successfully developed. In this study, neutron irradiation effects on mechanical properties of the innovative C C composites were examined. Materials used were one- and two-directionally reinforced composites with mesophase-pitch based carbon fibers as reinforcement and the mixture of green coke and phenolic resin as matrix precursor. Neutron irradiation was performed to 1.3 × 10 21 and 1.5 × 10 22 n/m 2 ( E > 1 MeV) at about 350 K. Mechanical properties were measured by bend tests. Flexural and shear strength were increased with increasing neutron fluence. On the contrary, fracture strain showed quite a little dependence on neutron fluence. Flexural modulus at near 0 strain was increased with increasing fluence. Stress stiffening at near 0 strain was suppressed with irradiation, while modulus drop was observed at high strain region and decreased with increasing neutron fluence. These results were interpreted in terms of microstructural change.

Effects of hydrogen on mechanical properties in irradiated austenitic stainless steels

To investigate the hydrogen effect on mechanical properties of solution annealed Type 304 stainless steel, tensile tests of neutron irradiated materials were conducted after a hydrogen charging and discharging process (hydrogen treatment). Elongation was less with increasing neutron fluence after hydrogen treatment than that of as-irradiated specimens. Intergranular cracking occurred by the hydrogen treatment in heavier irradiated specimens, in which the Cr depleted zone along grain boundary was observed. Embrittlement and intergranular cracking after the hydrogen treatment were estimated to be attributed to the Cr depleted zone at the grain boundary due to neutron irradiation.

Effects of radiations on the characteristics of alpha and fission tracks in CR-39 detectors

Abstract The effects of neutron, gamma and alpha radiations on the alpha and fission fragment tracks registration and revelation properties of CR-39 detectors (CR-39 and CR-39(DOP) were studied. It was found that the ratio of the bulk etch rate of irradiated to unirradiated (VG(irr.)/VG(unirr.) detectors is linearly dependent on dose. An exponential decrease in fission track densities with increase in neutron fluence was observed. The ratio of VG(irr.)/VG(unirr.) was found to be high in CR-39 than that in CR-39(DOP) exposed to the same reactor neutron fluence. The decrease in fission track densities with increase in neutron fluence was observed to be faster in CR-39 than in CR-39(DOP). This indicates that doping with dioctyl phthalate improves the radiation resistance of CR-39 detectors. It was observed that in detectors exposed to an alpha flux of the order of 9.36 × 106 / cm2, the fission track density was reduced by 11% and thereafter it remained constant. The results also indicate that thermal neutron...

Changes in the structure of poly (vinyl alcohol)-CrCl3 composites irradiated by low level fast neutron doses

Cast thin films of the composites PVA-CrCl3 were prepared. The absorption spectra, X-ray diffraction, hardness number and dielectric constant were measured before and after irradiation by neutrons in the fluence range of 3.4 × 105 to 1.68 × 108 n/cm2. The Racah constant was calculated to be 600 cm-1 which is about 65% of the free ion value. A pronounced band characterizing the carbonyl group has developed at 220 nm by irradiation. The degree of crystallinity is enhanced with the increase of neutron fluence. The position of the glass transition and α-relaxation temperatures were dependent on neutron fluence and doping content.

Radiation damage in triglycine sulphate due to fast neutron irradiation

Abstract The change in electrical properties of TGS crystals due to induced defects created by fast neutron irradiation of two different energies (2 and 14 MeV) and different integrated neutron fluxes have been studied in the vicinity of phase transition. It is observed that the electrical conductivity increases with increase of neutron fluence up to 1.7 × 1010 n · cm−2 and the values of the relative change of electrical conductivity in case of 2 MeV are higher than that of 14 MeV neutrons at the same neutron fluence (φ)

Effect of neutron irradiation on the strength of electron beam welded JFMS steel

Japanese ferritic-martensitic steel (JFMS) is a candidate material for nuclear fusion reactor application. It is material for high temperature use. Structural materials of the fusion reactor will be exposed to neutron irradiation. In order to research the fundamental properties of the material under irradiation, low temperature strength of JFMS steel and its electron beam welded joints were investigated under various irradiated conditions in this experiments. It was shown that strength decreases at low temperature in the base metal and, in electron beam welded joints of JFMS steel, increases with increasing neutron fluence.

Characteristics of the loop formation process in the MgO-Al 2O 3 system irradiated with fission neutrons

Magnesium aluminate spinel, MgAl2O4, has been identified to be resistant to void swelling during neutron irradiation. The microstructure controlling the swelling is investigated through characterization of the development of interstitial loops. Many clusters of 1/6〈111〉{111} are formed directly from damage cascades. However, the majority of these clusters are removed by the radiation-induced diffusion of structural vacancies. The surviving clusters become stable through the following process: 1/6〈111〉{111}→ 1/4〈110〉{111}→ 1/4〈110〉{101}→ 1/4〈110〉{110}→ 1/2〈110〉{110}. Aggregates of six equivalent 1/4〈110〉{110} and/or 1/2〈110〉{110} loops become dominant with increasing neutron fluence and/or irradiation temperature. This process reduces the self-energy of the loops through the compositional change of stacking faults, and the rotation of and the reactions between loops, and decreases the concentration of interstitials retained in the form of stable loops which bias vacancies and induce void swelling. The conclusion is that the reduced density of stable loops during damage cascades is caused by the dominant recombination of interstitials and structural vacancies and leads to a high resistance to void swelling under neutron irradiation.

Irradiation Effects on Corrosion Resistance and Microstructure of Zircaloy-4.

In order to investigate irradiation effects on nodular corrosion resistance of Zircaloy-4, an out-of-pile corrosion test was conducted using Zircaloy-4 specimens cut from the channel box of a fuel assembly irradiated in the BWR (Monticello reactor) up to the neutron fluence of 1.53×1026 n/m2 (E>1MeV). The corrosion test was carried out in high pressure steam of 10.3 MPa at 783 K for 24 h. No nodules appeared on the specimens cut from welded areas of the channel box and nodular corrosion resistance tended to be better with increasing neutron fluence. Microstructural evolution in the form of irradiation-induced release of Fe atoms from Zr(Fe, Cr)2 type precipitates was detected by an analytical electron microscope. It was found that the higher the concentration of dissolved Fe and Cr in the grains of Zircaloy-4, the better the nodular corrosion resistance.

The influence of fast neutron irradiation on the intra- and intergrain properties of the polycrystalline BiPbSrCaCuO system

The influence of irradiation by fast neutrons with fluences from 3.3 x 10 16 n/ cm 2 up to 3 x 10 18 n/ cm 2 on the physical properties of polycrystalline Bi 0.7 Pb 0.3 SrCaCu 1.8 O x was examined. Studies of DC magnetization, AC susceptibility, transport and thermoelectric power were performed. The irradiation caused a decrease of T c, determined from the onset of diamagnetism, by as much as 31 K for a fluence of 3 x 10 18 n/ cm 2. A strong influence of neutron irradiation on both intra- and intergranular properties was observed. The defects within the superconducting grains created by neutrons caused an increase of the pinning forces which enhanced the critical magnetization current. A gradual decoupling of Josephson weak links with increasing neutron fluence was observed in transport and low field magnetization measurements. From the AC susceptibility measurements the irreversibility lines between the flux-creep and flux-flow regions were determined. An increase of the absolute values of thermoelectric power with rising fluence was noticed.

Neutron-treated, ultrafast, photoconductor detectors

We have investigated homogeneous, photoconductive semiconductors as very fast radiation detectors. We irradiated GaAs, Cr-doped GaAs, and Fe-doped InP crystals with 14 MeV neutrons to produce lattice defects that act as fast recombination centers for electrons and holes. Using short-pulse lasers and 17 MeV linear-accelerator electrons and bremsstrahlung x rays, we measured the temporal response and sensitivity of these photoconductors as functions of fluence ranging from 1012 to 1016 neutrons/cm2. The carrier lifetime and mobility decrease monotonically as the neutron fluence increases, resulting in faster detector response at the expense of sensitivity. A resolving time of less than 30 ps (full width at half maximum) was measured for the above photoconductors irradiated with ∼1015 neutrons/cm2.

Precipitate stability in neutron-irradiated Zircaloy-4

Zircaloy-4, a zirconium-base alloy used extensively as cladding and core structural materials in water-cooled nuclear reactors, was examined by transmission electron microscopy, after neutron irradiation and postirradiation annealing. Phase instabilities found during irradiation at 561 K include the amorphous transformation and the dissolution of the intermetallic Zr(Fe,Cr) 2. The α-matrix is driven toward a single phase solid solution as the neutron fluence increases. This is evidenced by the continuous dissolution of the precipitate without precipitation of any new phase during irradiation. During postirradiation annealing at 833 K, solute Fe precipitates out particularly at the grain boundaries as Zr-Fe zeta-phase. Recrystallization of the amorphous precipitates occurs at a postirradiation annealing temperature of 1023 K. In general, the observed phenomena of amorphous transformation, precipitate dissolution, reprecipitation and recrystallization reflect the complex solute-point defect interactions in the α-matrix. The continuous solute dissolution during irradiation is expected to have a potential effect on irradiation growth, creep and corrosion properties of the alloy.

Microstructure and annealing behavior of heavily neutron-irradiated β-SiC

TEM studies were carried out on sintered β-SiC specimens which were irradiated in fast breeder reactors up to 1.0 × 10 27 n/m 2 (E > 0.1 MeV) at temperatures around 500°C. In SiC grains irradiated to 10 × 10 25 to 10 × 10 26 n/m 2 , unresolvable small black dots of 2 to 5 nm in size were observed. Change in microstructure occurred in the specimens irradiated to fluerices higher than 4.8 × 10 26 n/m 2 . Clear straight line contrast of dislocations 10 to 30 nm in length was observed, which might be Frank-type interstitial dislocation loops, lying on {111} planes. The size of defects was increased with increasing neutron fluence. Postirradiation annealing of specimens resulted in an increase in size and a decrease in the number density of defects. No void was observed. It is suggested that the dislocation loops observed in this experiment are not the cause of irradiation-induced swelling of SiC.

Low temperature neutron irradiation of the high-Tc-superconductors YBa2Cu3O7 and Y1.2Ba0.8CuO4

Abstract Single phase YBa 2 Cu 3 O 7 and multiphase Y 1.2 Ba 0.8 CuO 4 have been irradiated with fast reactor neutrons up to fluences of φt = 9.4 × 10 18 cm −2 ( E > 0.1 MeV). With increasing neutron fluence, we find an enhanced decrease of T c , considerable broadening of the transition width and an increase of ρ ( T = 100 K).

Effects of neutrons on some physical properties of cellulose nitrate for application in radiation dosimetry

The effects on some physical properties, such as hardness, DC electrical resistivity, optical density and luminescence emission, of cellulose nitrate sheets as tissue equivalent material by neutron fluences over the range 10 5–10 10 n cm −2 have been investigated. The data obtained indicate that the hardness of cellulose nitrate changes with increasing neutron fluence. This is attributed to change in molecular structure due to cross-linking followed by degradation. Electric resistivity, optical density, and luminescence emission intensity of the specimens exhibit linear responses on irradiation with neutrons. Semi-empirical formulae have been deduced which describe the changes in the above parameters. The application of this tissue equivalent material in neutron dosimetry has also been discussed.

Reduction of Plastic Anisotropy of Zircaloy Cladding by Neutron Irradiation, (I)

Knoop hardness was measured in order to study plastic anisotropy of irradiated fuel cladding tubes. Results are summarized as follows. The lowest Knoop hardness was obtained when the indenter was so oriented that {1010} ⟨1210⟩ prism slip played the dominant role in indentation formation. The dependence of Knoop hardness on neutron fluence implied that the damage caused by neutron irradiation affected the prism slip of α-zirconium more strongly. The considerable amount of plastic anisotropy observed in the unirradiated tubes showed a tendency to decrease with increasing neutron fluence.